Reusable launch vehicle attitude controls using time varying sliding modes.

摘要

In this thesis we present a multiple time scale Time-Varying Sliding Mode Control driven by a Sliding Mode Disturbance Observer (TV-SMC-SMDO) technique for reusable launch vehicle (RLV) attitude control. A fixed-gain SMC for RLVs has already been developed. Here we address the deficiencies of the fixed-gain SMC based Flight Control System (FCS) by avoiding saturation and improving controller robustness, thereby improving RLV performance.; The controller employs a body rate inner loop and an attitude outer loop, which are separated in time-scale by the singular perturbation principle. Both the sliding surface and the boundary layer dynamics are varied in real time using the PD-eigenvalue assignment technique. This salient feature is used to cope with saturation, which enhances the robustness and fault tolerance of the controller. The SMDO, which estimates external disturbances and model uncertainties, is used in the inner loop improving robustness of the continuous TV-SMC.